How to load older versions of a blend file?
By default blender will save 2 old versions whenever you save the blend file. That feature is what makes the .blend1 .blend2 flies. Read the bottom of gandalf3's answer here, for more info on the persistent save feature. The .blend1 will be in the same folder as the blend file it is a backup of.  

However if you do not have a backup blend, there is now way in blender to get back to a edit that has been saved over.